Ordering PHP array by number of identical objects - php

Question

Is there anyway to order an array in this way? For example if I had this array:
$array = array("foo", "bar", "item", "item", "foo", "foo");
And I wanted to order it so that it was "foo", "foo", "foo", "item", "item", "bar" is there any way to do that?

Answer 1

Would this do?
$array1 = array_count_values($array);
arsort($array1);
var_dump($array1);
will give you
array(3) {
["foo"]=>
int(3)
["item"]=>
int(2)
["bar"]=>
int(1)
}
or do you necessarily need them as repeated values? if yes, you may go for something like:
usort($array,create_function('$a,$b',
'return $GLOBALS["array1"][$a]<$GLOBALS["array1"][$b];'));
This is ugly code, but demonstrates the technique. It is also easy to make it good-looking with php 5.3 closures, but I don't know if you're on 5.3. That would look like this:
$acount=array_count_values($array = array("foo", "bar", "item", "item", "foo", "foo"));
usort($array,function($a,$b) use ($acount) { return $acount[$a]<$acount[$b]; });

Answer 2

First you have to count occurrence of each value (array_count_values), then use usort to sort element by your criteria:
<?php
$array = array('foo', 'bar', 'bar', 'foo', 'bar', 'foo', 'foobar', 'foo', 'foo', 'foobar', 'bar', 'foo');
$tmp = array_count_values($array);
usort($array, function($e1, $e2) use($tmp) {
return $tmp[$e2] - $tmp[$e1];
});
var_dump($array);

Answer 3

usort() could work. array_count_values() comes in handy though. With the calculations you need to make, this might be a little more clear and efficient . If there are a lot of repeated values (100+), you may also want to consider using array_fill() instead of the for loop:
function getSortedGroupArray($array) {
$return = array();
$values = array_count_values($array);
sort($values);
foreach($values as $count => $value) {
for($i = 0; $i < $count; ++$i) {
$return[] = $value;
}
}
return $return
}

Answer 4

That's quite and unusual sort process, it would be simplest to do as a two or three step process.
First count the different objects, then sort the object counts and generate from that the sorted object array.

Answer 5

Lets try this:
// First, lets count the number of objects
$sort_by_term = array();
foreach($array as $string)
{
if(isset($sort_by_term[$string]))
{
$sort_by_term[$string] += 1;
}
else
{
$sort_by_term[$string] = 1;
}
}
// Next let's sort them by number
$sort_by_count = array();
foreach($sort_by_term as $term => $count)
{
$sort_by_count[$count][] = $term;
}
// Now lets combine them
$final_array = array();
foreach($sort_by_count as $count => $term)
{
while($count > 0)
{
$final_array[] = $term;
$count -= 1;
}
}
Could be shortened using some of PHP's functions, but you get the idea of what has to be done.

Answer 6

You can use the following function for ordering by the frequency with which a value appears in an array:
function array_count_sort(&$array, $direction = 1)
{
// Could do with a better way of making $counts and $dir available to the
// sorting function, but this will do for illustrative purposes.
global $counts, $dir;
$counts = array_count_values($array);
$dir = $direction;
if (!function_exists('array_count_sort_cmp')) {
function array_count_sort_cmp($a, $b) {
global $counts, $dir;
$c = $counts[$a];
$d = $counts[$b];
if ($c == $d) return 0;
return ($c < $d) ? -$dir : $dir;
}
}
usort($array, 'array_count_sort_cmp');
}
And use it in the following way:
$test = array("foo", "bar", "item", "item", "foo", "foo");
print_r($test);
array_count_sort($test);
print_r($test);
array_count_sort($test, -1);
print_r($test);
which would yield
Array
(
[0] => foo
[1] => bar
[2] => item
[3] => item
[4] => foo
[5] => foo
)
Array
(
[0] => bar
[1] => item
[2] => item
[3] => foo
[4] => foo
[5] => foo
)
Array
(
[0] => foo
[1] => foo
[2] => foo
[3] => item
[4] => item
[5] => bar
)